How Do I solve the problem

A diver dives into a pool. His depth is given by the equation d = 0.5(t – 1)(t – 20), where d is his depth relative to ground level, and t is the time in seconds after he entered the water.
a) What is the length of time the driver travels before he resurfaces?

Question

How Do I solve the problem

A diver dives into a pool.  His depth is given by the equation d = 0.5(t – 1)(t – 20), where d is his depth relative to ground level, and t is the time in seconds after he entered the water.
a)  What is the length of time the driver travels before he resurfaces?

freethinker · Answer

can you try?

waheguru · Answer

I did but Im not sure

waheguru · Answer

We did this as an example in class and I wanted to ogver it

waheguru · Answer

The time he traveled is 19seconds but I dont understand why?

freethinker · Answer

did you copy the solution?

waheguru · Answer

0=0.5(t-1)(t-20)

t - 1 = 0

t = 1 

and

t - 20 = 0

t = 20

waheguru · Answer

Then we subtracted 20 - 1 which I did not understand

freethinker · Answer

why didn't you ask then?